1. Field of Invention
This invention relates to lasers and, more specifically, to lasers with configurable output beam characteristics. It also pertains to methods by which such lasers may be made to operate.
2. Description of Related Art
A laser source, or simply laser, is a source of radiation created by the amplification of light (visible or invisible electromagnetic radiation) through stimulated emission. Laser sources are characterized by their well-known unique emission characteristics, among these being wavelength, monochromaticity, coherence, beam directionality and brightness.
Lasers generally share the same four elements: a gain medium, a pump mechanism, a high-finesse cavity, and an output coupler. The gain medium provides light radiation amplification through amplified stimulated emission, the high-finesse cavity enables laser oscillation, the pump mechanism restores the gain medium energy thus allowing regenerative light amplification, and the output coupler enables the extraction of a fraction of the radiation contained within the high finesse cavity in the form of a useful laser output beam. The laser output beam has both spectral and spatial characteristics determined by the laser design. Practical laser devices may employ a high variety of gain media materials, pumping mechanisms and design approaches, and find usefulness in a wide range of applications.
Typically, a particular application requires a laser with well-defined output beam characteristics. Even within the same application, however, it is often required that these laser sources share a set of common specifications, but differ among themselves in only one relevant output beam characteristic. Consequently, it has generally been the case that each of the lasers needed to be individually custom designed to meet its respective specifications, sometimes entailing major design modifications and the attendant increased manufacturing costs and reduced flexibility.
A wavelength division multiplexing (WDM) telecommunication system is one well-known example of an application where several laser sources each with the same set of specifications, but respectively emitting at wavelengths different from one another are required. Conceptually this method increases the communication capacity by enabling the use of more than one optical carrier on a single fiber. In practice, WDM is accomplished by multiplexing the outputs of at least two lasers onto a single optical fiber. After transmission, at the receiving end, the reverse operation is performed allowing the multiple frequencies to be demultiplexed. To further expand the communication capability of each individual optical fiber, the WDM concept has been extended to enclose a set of closely-spaced wavelengths in the 1550 nm transmission window, such an implementation is referred to as dense wavelength division multiplexing (DWDM). The International Telecommunication Union (ITU) has established the use of a grid of frequencies in this window. The channels are anchored to a reference at 193.10 THz and equally spaced in frequency, the closely spaced grids having channels 100 GHz or a sub-multiple of that spacing, such as 50 GHz, 25 GHz, 12.5 GHz, or other.
Communication systems to implement this scheme thus must comprise laser sources that have emissions at each of the grid frequencies. This can be accomplished by having a multitude of different laser sources, each emitting at a frequency that matches one of the grid frequencies. The uninterrupted operation of such communication systems inherently requires a large volume of spare parts to be readily available on stock, which results in high running costs.